In my opinion the reason is that the code is not FORTRAN77 conform. I tried to overcome this problem by fixing the source code, there is an awful lot of wrong format statements. For finding the input files I changed in fs2fd.f:

infile = trim(dir_s)//trim(fil_s)
outfile = trim(dir_d)//trim(fil_d)

into

infile = './data/Nsat-fs.dat'
outfile = './data/Nsat-fd.dat'

Same in ins_d.f:

theofile = './data/Nsat-fd.dat'

Additionally in ins_d.f I had to move the passage

LOGICAL FIRST
DATA FIRST/.TRUE./

after the COMMON block:

COMMON/STCOMX/KM,BARY,PVSUN
LOGICAL FIRST
DATA FIRST/.TRUE./

FORTRAN77 seem not to support variable size arrays, so in isat_d.f I had to replace

dimension tp(np),up(np),cp(3,np),aia(4)

in line 183 with

dimension tp(100000),up(100000),cp(3,100000),aia(4)

The same for lines 2455 and 2456. In line 2408 I removed the definition of w(3,np,0:nd).
After that the source compiled into an executable called 'ilgs_d', which is ought to be the double precision version. The quad precision version would be called 'ilgs_q'. Anyway, the executable failed with the following output:

Second approach: f2c

Using f2c gives the same results as using f77. I hoped to get more insight from reading the C-code, but I did not. I had big success for the other IMCCE fortran programs with i2c, it helped me a lot in understanding and getting functional executables. But not this time.

Summary

The file ./data/Nsat-fd.dat exists, maybe the error refers to the file /DATA/DE403/de403.unx, which is indeed missing on my system. And I do not know from where to get it. At ftp://ssd.jpl.nasa.gov/pub/eph/planets/bsp/DE403.BSP I found the file for Sparc architecture, for i386 it seems not to be available any more, but it could be created from DE403.BSP.

But before doing further investigation I would like to ask a FORTRAN programmer about this software. My understanding is as follows, please correct me when I am wrong:

1) The software is a numerical integrator for a physical model of the Nepunian system. For as a period as long as the planet positions are provided, the Neptunian satellites position can be computed by numerical integration. Especially dates outside the interval 1800-2050 are no problem, when the DE403 planet positions are replaced by VSOP87 or similar.

2) Therefore it is possible to produce a large table of each satellites position and velocity for a long period, lets say 1500-2500. In fact this is the main goal. When I have this table, I will try frequency analysis techniques in order to create poisson series or similar, that can be included into stellarium.

My problem is that I can speak neigther french nor FORTRAN, so I really do not know what is going on in this software, and I would really appreciate your help. You can contact be by: